If it is stuck in one position, it probably has either a bad vacuum switch or a bad vacuum motor (brake).
To get at the parts ('94-'97) remove the ashtray and cup spiller. Remove the 2 screws behind each and remove the brackets that are held on.
Now to remove the vacuum switch, there are 4 (I think) screws holding it in place.
-OR-
Remove the dash panel under the steering wheel. On the side of the HVAC assembly the vacuum harness is attached and also has a junction. This is a handy place to check the vacuum brakes that you can see and you will be able to determine the colors of each vacuum hose.
Be forwarned: the manual claims that you have to remove the HVAC assembly to change any vacuum brakes other than the def. I think you might be able to get the floor brake if you get creative.
The best resource for this is a FSM (factor service manual) and you really should have one if it gets beyond a vacuum brake you can easily change or a switch. Good luck.